If I remember correctly there is a sending unit on the engine that senses low oil pressure that won't let the header lower. Had one go bad several years back that did that.
My old l would do this occasionally, never did figure it out for sure although I suspect it was a sticking poppet.. Would be cutting along fine and then just as you describe. Only cure was to shut combine "off" for 5 or 10 min for a "smoke break" and when restarted all was fine. by occasionally I mean once or twice a season.
If you have good currant to lower solinoid your safty switch and electrical is likely OK. You might want to swap raise and lower solinoids around. This would help eliminate bad coil or ground for coil. A quick check for electrical would be to install wire for raise to lower solinoid. Go into cab turn on key w_o starting and hit up button. If it lowers you have electrical problem. If not you have hydralic problem. There are many things that can be wrong hear. It would need good teardown of lower side of valve including the very tiny orfices and all o-rings. I have converted some of these earlier valves to eliminate one of the tiny orfices and enlarge size of the other one. These orfice sizes were increased in size a couple years after your machine was built. The large orfices will let a piece of contamination threw better. You might be better off picking up a working valve from salvage machine before getting to much into it. Any valve from '79 or earlier M or l will work. Maybe even some valves from the smaller machines of that era. Best of luck
i just had that problem on my l2.it was that sending unit.it was a oil pressure sending unit with two wires,just above the oil filters.hook them together to check,but replace if bad,its there for a reason.good luck
Thanks for all the info. Found the problem the popit valve was hung up on lower side. Put a small punch into ajusting hole that control how fast head drops, tapped with hammer. Works fine now but flustrating for a time.